Answer : The Greek word poly means many and meros means part or unit . Thus polymerization is the process of creating large molecules from six single molecules. That is, a reaction in which a large number of molecules of the same compound (e.g. , unsaturated hydrocarbons) combine to form new compounds with large molecules is called polymerization and the resulting compound is called polymer and the original compound is called monomer . For example , at high pressure ( 1000 - 1200 atm) and at a temperature of 100 - 200 ° C in the presence of little oxygen, polythene is produced by the addition of 600 - 1000 ethin molecules.